Given two binary strings a and b, return their sum as a binary string. Pattern focus: Bit Addition. Simulate binary addition with carry from the least significant bit to the most significant bit.
a, b = binary strings
binary string sum
Example 1:
Input:
a = "11" b = "1"
Output:
100
Explanation:
11 + 1 = 4, which is 100 in binary.
Example 2:
Input:
a = "1010" b = "1011"
Output:
10101
Explanation:
10 + 11 = 21, which is 10101 in binary.